Production activated carbon in dual pulse jet engine system

ABSTRACT

A particulate carbonaceous feedstock such as lignite is entrained and activated in the oscillating combustion gas in the two opposed tail pipes of the dual pulse-jet engine system. Gas continually withdrawn from the juncture of the two pipes contains entrained activated carbon which is subsequently separated from the gas.

United States Patent Belter et a1.

PRODUCTION ACTIVATED CARBON IN DUAL PULSE JET ENGINE SYSTEM Inventors:John W. Belter, Grand Forks, N. Dak.; Leroy Dockter, Laramie, Wyo.;Robert C. Ellman, East Grand Forks, Minn.

Assignee: The United States of America as represented by the Secretaryof the Interi- Filed: Nov. 9, 1970 Appl. No.: 87,759

US. Cl ..252/421, 23/209.4, 23/2091, 23/252, 23/2595, 23/284, 60/219,201/31, 201/35, 201/37, 201/38, 252/445 [451 June 6,1972

[56] References Cited UNITED STATES PATENTS 1,641,053 8/1927 Saver..252/421 2,851,337 9/1958 He1ler..... ....23/259.5 1,814,192 7/1931Slattengren.... ...23/259.5 1,475,502 11/1923 Manning..... ...20l/3l2,501,700 3/1950 Stuart .252/445 1,478,864 12/1923 Trent ..201/313,541,025 11/1970 Oda et al. ..252/421 2,769,692 11/1956 Heller..23/259.5

' Primary Examiner -Daniel E. Wyman Assistant ExaminerP. E. KonopkaAtt0rneyErnest S. Cohen and Howard Silverstein 57 ABSTRACT 8 Claims, 1Drawing Figure PATENTEDJUH 6 I972 3.6 6 8 14 5 INVENTORS JOHN l4. BELTER LEROY OOCKTER ROBERT C. ELLMAN ATTORNEYS PRODUCTION ACTIVATED CARBONIN DUAL PULSE JET ENGINE SYSTEM The invention relates to the productionof activated carbon also known as active carbon or activated charcoal.

Activated carbon has attained widespread and important use as anadsorbent. Heretofore it has been produced from particulate carbonaceousfeedstocks, such as lignite, anthracite, coconut shells, bone, etc., ina plurality of separate steps including drying, carbonization andactivation. A typical procedure is described in Activated Carbon by JohnW. Hassler, Chemical Publishing Company, Inc. 212 Fifth Avenue, NewYork, N.Y. 1963.

We have now discovered that such activated carbon can be produced in asingle step by the use of a dual pulse-jet combustion system. A detaileddescription of pulsating combustion is given in Pulsating Combustion,the Collected Works of F. H. Reynst, edited by M. W. Thring, Per

gamamon Press, 1961. On pages 27 and 86 of this book a dual pulse-jetsystem is shown wherein two single pulse-jet tubes or engines of thesame dimensions and configuration are located with the open end of theirrespective tail pipes immediately opposite one another so that the gasesbeing expelled by one tail pipe pass into the other. Under thisarrangement the jets will automatically work in opposed phase, i.e., onetube explodes while the other is drawing in air whereby the tubesreinforce the pulsations of each other. As used throughout thespecification and claims, the phrase dual pulse-jet" refers to such asystem. In the present invention a particulate carbonaceous feedstocksuch as lignite is injected into the tail pipes as the hot gases ofcombustion are oscillating back and forth within and between the pipes.As a result, the feed particles are carried back and forth in anentrained state and activated by the high temperatures therein.

At the juncture of the two pulse tubes, the pressure remainssubstantially above atmospheric, and a gas which contains entrainedactivated carbon is continually drawn off therefrom and separated into aparticulate product phase and a waste gas phase.

It is therefore an object of the present invention to employ the hotgases within the tail pipes of a dual pulse-jet combustion system toactivate a particulate carbonaceous material.

Another object is to produce activated carbon in a single step.

Other objects and advantages will be obvious from the following moredetailed description of the invention in conjunction with the drawing inwhich the figure shows a schematical view of the system of the presentinvention.

Referring to the drawing, reference numerals l and la represent twoidentically designed pulse jets. They are positioned so that theopenings 2 and 2a, respectively, in their tail pipe sections 3 and 3a,respectively, are immediately opposite one another within a commonplenum chamber 4. Propane or another liquid, solid, or gaseous fuelsuitable for pulse-jets is injected into combustion chambers 5 and 5athrough conduits 6 and 6a, respectively, together with compressedstart-up air conveyed into the chambers by conduits 7 and 7a.

Ignition devices, 8 and 8a, such as a spark plug in each chamber, thenignite the air-fuel mixture, after which selfsustained pulsatingcombustion is carried on, in the prior art manner, in each pulse-jet.Throughout the operation, combustion air is drawn into the combustionchambers, during each suction cycle, through conduits 9 and 9a.

Tuning of the pulse-jets is automatic whereby one jet is exploding andexpelling gases as the other is drawing in gases including combustionair. Thereafter any particulate carbonaceous material which hasheretofore been employed to manufacture activated carbon is continuouslyslowly fed by, for example, a screw feeder into one or both tail pipes 3and 3a through conduits l0 and 10a, respectively.

Pulsating hot gases in the tail pipes entrain the particulate feedstockand propel it back and forth within and between the pipes. At thejuncture of the pipes within plenum 4, the pressure is positive, and anet flow of gas containing entrained particles of product is continuallyallowed to pass out of the system into the plenum 4 and then throughconduit 11 to a cyclone separator 12. Activated carbon is collected invessel 13 below the separator while gas is taken off at conduit 14.

Although the tail pipes are shown with their open ends spaced apart fromanother, these en could be integrated together with an exit conduitextending therefrom so as to provide greater control over the residencetime of the particles in the activation zone.

During activation in the tail pipes, the feedstock undergoes severalchanges which have heretofore been accomplished in a plurality of units.That is, the particles are substantially dried out and they lose some oftheir volatile matter to create pores on the particle surface.Thereafter the pore surface reacts with steam and/or CO When as-minedlignite is employed as the feed material, there is sufficient moisturepresent in the feedstock to accomplish this latterieactiofi in the h'ottail pipes.

However, some particulate feedstocks such as subbituminous coal do notcontain sufficient moisture, and it is then necessary to inject steamand/or CO along with the feedstock. One manner of employing steam, forexample, is to mix water with the feedstock and introduce it as aslurry. Another method is to employ part of a combustion zone or zonesin the system as a steam generator wherein a water tube runs through theair inlet 9 and/or 9a into the respective combustion chamber, and opensinto the tail pipe section. Alternatively, the combustion chamber can besurrounded by a coil or jacket for steam generation after which thesteam is injected into the tail pipes. A further alternative involvesinjecting a granular material together with the feedstock, whichmaterial decomposes at the operating temperatures to steam and/or carbondioxide. Still further, moisture can be supplied if a solid, moisturecontaining material is employed as the jet fuel.

For any particular dual pulse-jet structure, the amount of jet fuelwhich is supplied the system affects the operating temperatures and,thereby, product quality. Further, the continual rate at which theparticulate feedstock is injected affects the gas-to-solids ratio in theactivation zone. Product quality is also affected by the rate at whichgas and entrained product are removed from the tail pipes. Optimumoperating conditions are best determined experimentally for eachfeedstock and structure.

As indicated previously, pulse-jets operate on liquid, gaseous and solidfuels. A discussion of solid fuel operations is given in preprint No.WA69FU4 of the A.S.M.E., for the 1969 Winter Annual meeting of A.S.M.E.at Los Angeles, California, November, 1969 which preprint is entitledOperating Experience with Lignite Fueled Pulse-Jets." Other fuelsinclude propane, gasoline, oil, or bituminous coal.

The following example illustrates the effectiveness of the process ofthe present invention.

EXAMPLE Two identical pulse-jets, each similar to the one described inlntemational Coal Preparation Congress", Fifth Congress, Pittsburgh,Pa., October 3-7, 1966, page 465, FIG. 1, were arranged with theopenings in the tail pipes opposite one another and spaced apart 6inches. A 55 gallon plenum vessel surrounded the juncture of the twopipes and the vessel had a 4 inch conduit leading to a cycloneseparator.

Pulsating combustion was established with propane supplied at 15 psigthrough a manifold system to the combustion chambers. Lignite was thensupplied at a rate of about 200 No./hr to one of the tail pipes at apoint 6 feet from the open end of the pipe. The particle size of thelignite was about oneeighth inch and finer. Activated carbon product wascollected at the cyclone separator at a rate of about 70 lb per hr. Somefine carbon was lost in the discharge gases.

Several tests were conducted with various [ignites having a compositionranging from 29 percent moisture and 29 percent volatile matter tolignite char having essentially 0 percent moisture and 20.0 percentvolatile matter MAF. To effect temperature variations during the tests,the jet fuel inlet pressure was controlled by valves in the lines toeach engine. Only the exit gas temperature at the juncture of the tailpipes was measured during the tests, although much higher temperaturesobviously occurred within the shock waves in the pipes.

Satisfactory results were obtained in all these tests. As an example,when employing lignite having 29 percent moisture and 29 percentvolatile matter, wherein the jet fuel was introduced at such a rate sothat the temperature of the gas exiting from the plenum vessel was l,lOF, the product had only 0.3 percent moisture and 28 percent volatilematter MAF. Using the iodine absorption test for activation evaluation,the product compared favorably with industrial-grade activated carbon.In additional tests, optimum results were obtained whenmoisture-containing char was slurred in water and then introduced intothe pulse-jets.

Treating the feedstock in a pulsating atmosphere of hot gases hasseveral advantages. First, the gas-particle relative velocity changessweep the particle surface allowing increased heat and mass exchange.Further, pressure oscillations have a pumping effect on the volatileswithin the particles which helps to partially remove such volatiles fromthe particles. Still further, very high temperatures occur within eachshock wave although the nominal gas temperature may remain low. Thislatter phenomena" is discussed in the Journal of the Institute of Fuel,September, 196'] pages 359-367.

By employing a dual-pulsed system as opposed to a single pulse jet,several advantages accrue. For example, the feedstock particles are notimmediately expelled, and they thus have a high probability of manytransits from one tail pipe to another so that sufficient residence timeis encountered to accomplish the desired reactions. Further, dualpulse-jet engines mutually reinforce the pressure waves of one anotherwhich intensifies the above-mentioned pressure oscillations, andproduces higher peak temperatures in the shock waves. Further, themagnitude of the gas-particle relative velocity changes is increased bymore intense pulsations since such increases in intensity will raise theacceleration experienced by the feedstock particles either by simpletranslational motions or by being spun in velocity gradients.

In the prior art, several units have often been employed,

sometimes batch units, to produce activated carbon, involving residencetimes of several hours. in comparison, the single stage, continuoussystem of the present invention rapidly produces activated carbon. Lowcost pulse-jet engines deliver extremely high heat release rates, andthe pulsating flow allows this intense heat to be rapidly transferred tothe feedstock. Thus, by the present invention, activated carbon can beproduced on a large scale at low costs and is thus suitable forapplications which have heretofore not employed activated carbon becauseof economics. For example, Extension Bulletin E-668, September, 1969, ofthe Michigan State University Cooperative Extension Service describesthe use of activated carbon as a food for cows to prevent pesticidecontamination in milk and meat. In the bulletin it was recognized thatsuch treatment would be at a high cost considering the then prevailingprice of the activated carbon.

The present invention, furthermore, would broaden the use of lignite (alittle used national resource) and other coals as well.

What is claimed is:

1. In a process for producing activated carbon from a solid particulatecarbonaceous feedstock the improvement comprising entraining saidfeedstock in the oscillating hot combustion gas in the tail pipes of adual pulse jet combustion system in the presence of steam or COwithdrawing from said system, at the juncture of said tail pipes, a gascontaining entrained particles of activated carbon; and separating saidactivated carbon from said withdrawn gas.

2. The process of claim 1 wherein said feedstock is lignite.

3. The process of claim 1 wherein said feedstock is slurried in waterwhen supplied to said tailpipcs.

4. The process of claim 1 wherein said pulse-jet system is employed togenerate steam, and then said steam is injected into said tailpipes.

5. The process of claim 1 wherein a granular material, which decomposesinto steam or CO at the temperature of said hot combustion gas, isinjected into said tailpipes with said feedstock.

6. The process of claim 3 wherein said feedstock is lignite.

7. The process of claim 4 wherein said feedstock is lignite.

8. The process of claim 5 wherein said feedstock is lignite.

2. The process of claim 1 wherein said feedstock is lignite.
 3. Theprocess of claim 1 wherein said feedstock is slurried in water whensupplied to said tailpipes.
 4. The process of claim 1 wherein saidpulse-jet system is employed to generate steam, and then said steam isinjected into said tailpipes.
 5. The process of claim 1 wherein agranular material, which decomposes into steam or CO2 at the temperatureof said hot combustion gas, is injected into said tailpipes with saidfeedstock.
 6. The process of claim 3 wherein said feedstock is lignite.7. The process of claim 4 wherein said feedstock is lignite.
 8. Theprocess of claim 5 wherein said feedstock is lignite.